Semiconductor device and method

ABSTRACT

In an embodiment, a method includes: forming a first fin extending from a substrate; forming a second fin extending from the substrate, the second fin being spaced apart from the first fin by a first distance; forming a metal gate stack over the first fin and the second fin; depositing a first inter-layer dielectric over the metal gate stack; and forming a gate contact extending through the first inter-layer dielectric to physically contact the metal gate stack, the gate contact being laterally disposed between the first fin and the second fin, the gate contact being spaced apart from the first fin by a second distance, where the second distance is less than a second predetermined threshold when the first distance is greater than or equal to a first predetermined threshold.

PRIORITY CLAIM AND CROSS-REFERENCE

This application is a continuation of U.S. patent application Ser. No.17/862,628 filed Jul. 12, 2022, entitled “Semiconductor Device andMethod,” which is a continuation of U.S. patent application Ser. No.17/169,809 filed Feb. 8, 2021, entitled “Semiconductor Device andMethod,” now U.S. Pat. No. 11,393,724 issued on Jul. 19, 2022, which isa continuation of U.S. patent application Ser. No. 16/567,053 filed Sep.11, 2019 entitled “Semiconductor Device and Method,” now U.S. Pat. No.10,957,604 issued on Mar. 23, 2021, which claims the benefit of U.S.Provisional Application No. 62/753,456, filed on Oct. 31, 2018, whichapplications are hereby incorporated herein by reference.

BACKGROUND

Semiconductor devices are used in a variety of electronic applications,such as, for example, personal computers, cell phones, digital cameras,and other electronic equipment. Semiconductor devices are typicallyfabricated by sequentially depositing insulating or dielectric layers,conductive layers, and semiconductor layers of material over asemiconductor substrate, and patterning the various material layersusing lithography to form circuit components and elements thereon.

The semiconductor industry continues to improve the integration densityof various electronic components (e.g., transistors, diodes, resistors,capacitors, etc.) by continual reductions in minimum feature size, whichallow more components to be integrated into a given area. However, asthe minimum features sizes are reduced, additional problems arise thatshould be addressed.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIGS. 1A, 1B, 1C, 2A, 2B, 2C, 2D, 3A, 3B, 3C, 4A, 4B, 4C, 5A, 5B, 5C,6A, 6B, and 6C illustrate intermediate stages in the manufacturing ofFinFETs, in accordance with some embodiments.

FIGS. 7A and 7B illustrate a gate contact layout, in accordance withsome embodiments.

FIG. 8 illustrates experimental data for a gate contact layout, inaccordance with some embodiments.

FIGS. 9A and 9B illustrate a gate contact layout, in accordance withsome other embodiments.

FIGS. 10 through 13 illustrate a gate contact layout, in accordance withsome other embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the invention. Specificexamples of components and arrangements are described below to simplifythe present disclosure. These are, of course, merely examples and arenot intended to be limiting. For example, the formation of a firstfeature over or on a second feature in the description that follows mayinclude embodiments in which the first and second features are formed indirect contact, and may also include embodiments in which additionalfeatures may be formed between the first and second features, such thatthe first and second features may not be in direct contact. In addition,the present disclosure may repeat reference numerals and/or letters inthe various examples. This repetition is for the purpose of simplicityand clarity and does not in itself dictate a relationship between thevarious embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

In accordance with some embodiments, metal gate stacks are formed overfins, and gate contacts are formed to the metal gate stacks. In someembodiments, voids form in the metal gate stacks. The spacing betweenthe gate contacts and fins is constrained according to the spacingbetween adjacent fins. The spacing between the gate contacts and ends ofthe metal gate stack lines is also constrained. The spacing isconstrained to a value that is less than a distance at which voidstypically form in the metal gate stack. Formation of the gate contactson the voids may thus be avoided. Further, in some embodiments, themetal gate stack lines are cut during formation to avoid the formationof voids.

FIGS. 1A through 6C illustrate intermediate stages in the manufacturingof FinFETs, in accordance with some embodiments. FIGS. 1A, 2A, 3A, 4A,5A, and 6A are three-dimensional views. FIGS. 1B, 2B, 3B, 4B, 5B, and 6Bare cross-sectional views shown along a longitudinal axis of theFinFETs, e.g., perpendicular to the direction of current flow betweenthe source/drain regions of the FinFETs, and are shown for a singleFinFET. FIGS. 1C, 2C, 3C, 4C, 5C, and 6C are cross-sectional views shownalong a latitudinal axis of the FinFETs, e.g., parallel to the directionof current flow between the source/drain regions of the FinFETs, and areshown for a single FinFET. FIG. 2D is a cross-sectional view shown alonga longitudinal axis of the FinFETs, through source/drain regions of theFinFETs.

Some embodiments discussed herein are discussed in the context ofFinFETs formed using a gate-last process. In other embodiments, agate-first process may be used. Also, some embodiments contemplateaspects used in planar devices, such as planar FETs.

In FIGS. 1A through 1C, a substrate 50 is provided. The substrate 50 maybe a semiconductor substrate, such as a bulk semiconductor, asemiconductor-on-insulator (SOI) substrate, or the like, which may bedoped (e.g., with a p-type or an n-type dopant) or undoped. Thesubstrate 50 may be a wafer, such as a silicon wafer. Other substrates,such as a multi-layered or gradient substrate may also be used. Oneregion of the substrate 50 is illustrated, which can be for formingn-type devices (such as NMOS transistors, e.g., n-type FinFETs) or forforming p-type devices (such as PMOS transistors, e.g., p-type FinFETs).The substrate 50 may include multiple, physically separated regions, inwhich any number of device features (e.g., other active devices, dopedregions, isolation structures, etc.) may be formed.

Further, fins 52 are formed extending from the substrate 50. The fins 52are semiconductor strips. In the embodiment shown, the fins 52 are anepitaxially grown semiconductor material, different from the material ofthe substrate 50. The fins 52 may be formed from silicon, silicongermanium (Si_(x)Ge_(1−x), where x can be in the range of 0 to 1),silicon carbide, pure or substantially pure germanium, a III-V compoundsemiconductor, a II-VI compound semiconductor, or the like. For example,the available materials for forming III-V compound semiconductorinclude, but are not limited to, InAs, AlAs, GaAs, InP, GaN, InGaAs,InAlAs, GaSb, AlSb, AlP, GaP, and the like. In the embodiment shown, thefins 52 are formed by epitaxially growing a layer of the semiconductormaterial on the substrate 50, and then etching trenches 54 in thesemiconductor material, with the fins 52 being formed from portions ofthe semiconductor material that remain unremoved. The etching may be anyacceptable etch process, such as a reactive ion etch (RIE), neutral beametch (NBE), the like, or a combination thereof. The etch may beanisotropic. In other embodiments, the fins 52 are the same material asthe substrate 50, and are formed by etching trenches in the substrate50. As discussed below, the fins 52 are used, to form channel regions ofFinFETs. Although only two fins 52 are illustrated, it should beappreciated that any number of fins 52 may be formed.

The fins 52 may be patterned by any suitable method. For example, thefins 52 may be patterned using one or more photolithography processes,including double-patterning or multi-patterning processes. Generally,double-patterning or multi-patterning processes combine photolithographyand self-aligned processes, allowing patterns to be created that have,for example, pitches smaller than what is otherwise obtainable using asingle, direct photolithography process. For example, in one embodiment,a sacrificial layer is formed over a substrate and patterned using aphotolithography process. Spacers are formed alongside the patternedsacrificial layer using a self-aligned process. The sacrificial layer isthen removed, and the remaining spacers may then be used to pattern thefins.

The fins 52 are formed to a width W₁ at the surface of the substrate 50.In some embodiments, the width W₁ is in the range of about 6 nm to about600 nm. Additionally, the fins 52 are spaced apart from each other by adistance D₁. By spacing the fins 52 in such a fashion, the fins 52 mayeach form a separate channel region while still being close enough toshare a common gate. As discussed further below, the distance D₁ isselected in such a way as to help reduce the contact resistance (R_(c))of subsequently formed contacts to the gate of the FinFETs. In someembodiments, the distance D₁ is large, such as in the range of about 22nm to about 800 nm. In some embodiments, the distance D₁ is small, suchas in the range of about 22 nm to about 200 nm.

Further, shallow trench isolation (STI) regions 56 are formed betweenthe fins 52. The STI regions 56 may be formed by filling the trenches 54with a dielectric material and recessing the dielectric material in thetrenches 54 to form the STI regions 56. The dielectric material may bean oxide material, a high-density plasma (HDP) oxide, or the like. Thedielectric material may be formed, after an optional cleaning and liningof the trenches 54, using either a chemical vapor deposition (CVD)method, a high density plasma CVD method, or other suitable method offormation as is known in the art.

The trenches 54 may be filled by overfilling the trenches 54 and thesubstrate 50 with the dielectric material and then removing the excessmaterial outside of the trenches 54 and the fins 52 through a suitableprocess such as chemical mechanical polishing (CMP), an etch, acombination thereof, or the like. In an embodiment, the removal processremoves dielectric material overlying the fins 52, so that top surfacesof the fins 52 are exposed.

Once the trenches 54 have been filled with the dielectric material, thedielectric material may then be recessed from the top surfaces of thefins 52. The recessing may be performed to expose at least a portion ofthe sidewalls of the fins 52 adjacent to the top surfaces of the fins52. The dielectric material may be recessed using a wet etch by dippingthe top surfaces of the fins 52 into an etchant such as HF, althoughother etchants, such as H₂, and other methods, such as a reactive ionetch, a dry etch with etchants such as NH₃/NF₃, chemical oxide removal,or dry chemical clean may be used. The dielectric material is recessedsuch that the exposed portions of the fins 52 have a first height H₁. Insome embodiments, the first height H₁ is in the range of about 40 Å toabout 100 Å. Additionally, the recessing may also remove any leftoverdielectric material located over the fins 52, exposing the fins 52 forfurther processing.

In FIGS. 2A through 2C, dummy gate dielectrics 58 and dummy gateelectrodes 60 are formed over each of the fins 52. In some embodiments,a dummy gate dielectric layer is formed by thermal oxidation, chemicalvapor deposition, sputtering, or any other methods known and used in theart for forming dielectric layers. A dummy gate electrode layer is thenformed on the dummy gate dielectric layer. The dummy gate electrodelayer may be formed from a conductive material such aspolycrystalline-silicon (polysilicon), poly-crystallinesilicon-germanium (poly-SiGe), metallic nitrides, metallic silicides,metallic oxides, metals, or the like, and may be formed by a depositionprocess such as physical vapor deposition (PVD), chemical vapordeposition (CVD), sputter deposition, or the like. The dummy gateelectrode layer and dummy gate dielectric layer are then patterned, suchas by acceptable photolithography and etching processes, with remainingportions of the dummy gate dielectric layer and dummy gate electrodelayer, respectively, forming the dummy gate dielectrics 58 and dummygate electrodes 60.

Further, gate spacers 62 are formed on opposing sides of the dummy gateelectrodes 60, over each of the fins 52. In some embodiments, the gatespacers 62 are formed by blanket depositing a spacer layer, such as alayer of silicon nitride, silicon oxide, silicon oxynitride, siliconcarbide, or the like by a deposition process such as CVD or plasmaenhanced CVD (PECVD). The spacer layer is then patterned, such as by oneor more etches to remove horizontal portions of the spacer layer, withremaining vertical portions of the spacer layer forming the gate spacers62.

Further, epitaxial source/drain regions 64 are formed in the fins 52,such that each dummy gate electrode 6 o is laterally disposed betweenrespective neighboring pairs of the epitaxial source/drain regions 64.The epitaxial source/drain regions 64 exert stress in what will be thechannel regions of the resulting FinFETs, thereby improving performance.The gate spacers 62 separate the epitaxial source/drain regions 64 fromthe dummy gate electrodes 60 by an appropriate lateral distance so thatthe epitaxial source/drain regions 64 do not short out subsequentlyformed gates of the resulting FinFETs. The epitaxial source/drainregions 64 are formed by etching recesses in the fins 52. Then, theepitaxial source/drain regions 64 in the region are epitaxially grown inthe recesses. The epitaxial source/drain regions 64 may include anyacceptable material, such as appropriate for n-type or p-type FinFETs.For example, when n-type FinFETs are formed, the epitaxial source/drainregions 64 may include materials exerting a tensile strain in thechannel region of the fins 52, such as silicon, SiC, SiCP, SiP, or thelike. Likewise, when p-type FinFETs are formed, the epitaxialsource/drain regions 64 may include materials exerting a compressivestrain in the channel region of the fins 52, such as SiGe, SiGeB, Ge,GeSn, or the like. The epitaxial source/drain regions 64 may havesurfaces raised from respective surfaces of the fins 52 and may havefacets.

As a result of the epitaxy processes used to form the epitaxialsource/drain regions 64, upper surfaces of the epitaxial source/drainregions 64 have facets which expand laterally outward beyond sidewallsof the fins 52. In the embodiment shown in FIGS. 2A through 2C, adjacentepitaxial source/drain regions 64 remain separated after the epitaxyprocess is completed. In other embodiments, such as that shown in FIG.2D, these facets cause adjacent epitaxial source/drain regions 64 of asame FinFET to merge.

In FIGS. 3A through 3C, a first inter-layer dielectric (ILD) 66 isdeposited over the substrate 50. The first ILD 66 may be formed of adielectric material, and may be deposited by any suitable method, suchas CVD, PECVD, or flowable CVD (FCVD). Dielectric materials may includePhospho-Silicate Glass (PSG), Boro-Silicate Glass (BSG), Boron-DopedPhospho-Silicate Glass (BPSG), undoped Silicate Glass (USG), or thelike. Other insulation materials formed by any acceptable process may beused. In some embodiments, a contact etch stop layer (CESL) is disposedbetween the first ILD 66 and the epitaxial source/drain regions 64, thegate spacers 62, and the dummy gate electrodes 60. The CESL may comprisea dielectric material, such as, silicon nitride, silicon oxide, siliconoxynitride, or the like, having a different etch rate than the materialof the first ILD 66. In some embodiments, a planarization process, suchas a CMP, is performed to level the top surface of the first ILD 66 withthe top surfaces of the dummy gate electrodes 60 and the gate spacers62.

In FIGS. 4A through 4C, the dummy gate electrodes 60 and dummy gatedielectrics 58 are removed in one or more etching step(s), so thatrecesses 68 are formed. Each recess 68 exposes a channel region of arespective fin 52. Each channel region is laterally disposed betweenneighboring pairs of the epitaxial source/drain regions 64. During theremoval, the dummy gate dielectrics 58 may be used as etch stop layerswhen the dummy gate electrodes 60 are etched. The dummy gate dielectrics58 may then be optionally removed after the removal of the dummy gateelectrodes 60.

In FIGS. 5A through 5C, gate dielectrics 70 and gate electrodes 72 areformed for replacement gates. The gate dielectrics 70 are conformallydeposited in the recesses 68, such as on the top surfaces and thesidewalls of the fins 52 and on sidewalls of the gate spacers 62. Thegate dielectrics 70 may also be formed on top surfaces of the first ILD66. In accordance with some embodiments, the gate dielectrics 70comprise silicon oxide, silicon nitride, or multilayers thereof. In someembodiments, the gate dielectrics 70 include a high-k dielectricmaterial, and in these embodiments, the gate dielectrics 70 may have a kvalue greater than about 7.0, and may include a metal oxide or asilicate of Hf, Al, Zr, La, Mg, Ba, Ti, Pb, and combinations thereof.The formation methods of the gate dielectrics 70 may includeMolecular-Beam Deposition (MBD), atomic layer deposition, PECVD, and thelike. In embodiments where portions of the dummy gate dielectrics 58remain in the recesses 68, the gate dielectrics 70 include a material ofthe dummy gate dielectrics 58 (e.g., SiO₂).

The gate electrodes 72 are deposited over the gate dielectrics 70,respectively, and fill the remaining portions of the recesses 68. Thegate electrodes 72 may include a metal-containing material such as TiN,TiO, TaN, TaC, Co, Ru, Al, W, combinations thereof, or multi-layersthereof. The gate electrodes 72 may be formed by a deposition processsuch as atomic layer deposition (ALD). The gate electrodes 72 mayinclude any number of liner layers, work function tuning layers, andfill materials. After the filling of the gate electrodes 72, aplanarization process, such as a CMP, may be performed to remove theexcess portions of the gate dielectrics 70 and the material of the gateelectrodes 72, which excess portions are over the top surface of thefirst ILD 66. The remaining portions of material of the gate electrodes72 and the gate dielectrics 70 thus form replacement gates of theresulting FinFETs. The gate electrodes 72 and the gate dielectrics 70may be collectively referred to as gate stacks 74. The gate stacks 74extend along sidewalls of a channel region of the fins 52.

After formation, the gate stacks 74 have a width W₂. In someembodiments, the width W₂ is in the range of about 6 nm to about 300 nm.As discussed further below, the distance D₁ between the fins 52 (seeFIG. 1A) is selected according to the width W₂ of the gate stacks 74that are formed.

In FIGS. 6A through 6C, a second ILD 76 is deposited over the first ILD66. In some embodiments, the second ILD 76 is a flowable film formed bya flowable CVD method. In some embodiments, the second ILD 76 is formedof a dielectric material such as PSG, BSG, BPSG, USG, or the like, andmay be deposited by any suitable method, such as CVD and PECVD.

Further, gate contacts 78 and source/drain contacts 80 are formedthrough the second ILD 76 and the first ILD 66. Openings for thesource/drain contacts 80 are formed through the first ILD 66 and secondILD 76, and openings for the gate contacts 78 are formed through thesecond ILD 76 (and optionally the gate mask, if formed). The gatecontacts 78 (or source/drain contacts 80) may include a liner (such as adiffusion barrier layer, an adhesion layer, or the like) and aconductive material. The openings may be formed using acceptablephotolithography and etching techniques. The liner and the conductivematerial are formed in the openings. The liner may include titanium,titanium nitride, tantalum, tantalum nitride, or the like. Theconductive material may be copper, a copper alloy, silver, gold,tungsten, cobalt, aluminum, nickel, or the like. The conductive materialmay be formed by a deposition process such as CVD. A planarizationprocess, such as a CMP, may be performed to remove excess material froma surface of the second ILD 76. The remaining liner and conductivematerial forms the source/drain contacts 80 and gate contacts 78 in theopenings. An anneal process may be performed to form a silicide at theinterface between the epitaxial source/drain regions 64 and thesource/drain contacts 80. The source/drain contacts 8 o are physicallyand electrically coupled to the epitaxial source/drain regions 64, andthe gate contacts 78 are physically and electrically coupled to the gateelectrodes 72. The source/drain contacts 80 and gate contacts 78 may beformed in different processes, or may be formed in the same process.Although shown as being formed in the same cross-sections, it should beappreciated that each of the source/drain contacts 80 and gate contacts78 may be formed in different cross-sections, which may avoid shortingof the contacts.

After formation, the gate contacts 78 have a width W₃. In someembodiments, the width W₃ is in the range of about 10 nm to about 20 nm.As discussed further below, dimensions of the gate stacks 74 areselected according to the width W₃ of the gate contacts 78.

FIGS. 7A and 7B illustrate a gate contact 78 layout, in accordance withsome embodiments. FIGS. 7A and 7B are top-down views, showing somefeatures of the structure of FIG. 6A through 6C. In particular, multiplegate stacks 74 are shown, with each respective gate stack 74 extendingover two fins 52. The gate contacts 78 physically couple the gate stacks74, and are disposed a distance D₂ from a closest one of the fins 52.FIG. 7A shows a scenario where the distance D₁ between the fins 52 issmall, e.g., where the distance D₁ is less than a predeterminedthreshold (discussed further below). As discussed above, a smalldistance D₁ can be in the range of about 22 nm to about 200 nm. FIG. 7Bshows a scenario where the distance D₁ between the fins 52 is large,e.g., where the distance D₁ is greater than the predetermined threshold(discussed further below). As discussed above, a large distance D₁ canbe in the range of about 22 nm to about 800 nm.

The width W₂ of the gate stacks 74 is sometimes referred to as thecritical dimension of the gate stacks 74. At smaller criticaldimensions, portions of the gate stacks 74 may be deformed. FIG. 7B is atop-down view of deformed gate stacks 74. The deformed gate stacks 74each include a void 82. Portions of the gate stacks 74 deform becausethe coefficient of thermal expansion (CTE) of the gate stacks 74 issmaller than the CTE of surrounding dielectric materials (e.g., of thefirst ILD 66 and STI regions 56 (see FIGS. 6A through 6C)). Afterthermal processing, the surrounding dielectric may shrink more than thefins 52. The shrinking of the surrounding dielectric pulls apart thegate stacks 74, causing the voids 82 to be formed. The amount ofdeformation depends on the volume of the surrounding dielectric.Portions of the gate stacks 74 distal the fins 52 are surrounded by agreater volume of dielectric, and so more deformation of these portionsoccurs. Portions of the gate stacks 74 proximate the fins 52 aresurrounded by a lesser volume of dielectric, and so less (orsubstantially no) deformation of these portions occurs. When thedistance D₁ between fins 52 is small (as in FIG. 7A), substantially nodeformation of the gate stacks 74 occurs between the fins 52. When thedistance D₁ between fins 52 is large (as in FIG. 7B), deformation of thegate stacks 74 occurs between the fins 52.

Because of deformation, the gate stacks 74 have multiple widths. Thewidth W₂ of the gate stacks 74 is the width of the un-deformed portionsof the gate stacks 74, e.g., the widths of the portions over the fins52. In other words, the width W₂ is the narrowest width the gate stacks74, as measured at the narrowest portions of the gate stacks 74.

Formation of the voids 82 does not prevent the gate stacks 74 fromproperly functioning. However, the voids 82 have a high k-value bynature of being air or a vacuum. Forming the gate contacts 78 on thevoids 82 results in an increased interface resistance between the gatecontacts 78 and gate stacks 74. The contact resistance (R_(c)) of thegate contacts 78 is largely determined by the interface resistancebetween the gate contacts 78 and gate stacks 74, and that interfaceresistance may increase with smaller contact areas, e.g., when the gatestacks 74 are small. The contact area may be further reduced when thegate contacts 78 are on the voids 82, thus increasing the contactresistance of the gate contacts 78.

In accordance with some embodiments, the gate contacts 78 are formedphysically coupling portions of the gate stacks 74 that aresubstantially free from voids 82. The contact area of the gate contacts78 may thus be increased, thereby decreasing the contact resistance ofthe gate contacts 78. During a design process, the distance D₂ isdetermined according to the distance D₁. In particular, when thedistance D₁ is greater than a first predetermined threshold T₁, thedistance D₂ is constrained to be less than a second predeterminedthreshold T₂. FIG. 7A shows a scenario where the distance D₁ is lessthan the first predetermined threshold T₁, and so the distance D₂ isunconstrained. FIG. 7B shows a scenario where the distance D₁ is greaterthan the first predetermined threshold T₁, and so the distance D₂ isconstrained. The first predetermined threshold T₁ and secondpredetermined threshold T₂ are defined as multiples of the width W₂ ofthe gate stacks 74. In some embodiments, the first predeterminedthreshold T₁ is in a range of about 35 to about 40 times the width W₂ ofthe gate stacks 74, and the second predetermined threshold T₂ is in arange of about 10 to about 13 times the width W₂ of the gate stacks 74.Further, a ratio of the first predetermined threshold T₁ to the secondpredetermined threshold T₂ can be in the range of about 3 to about 5.

FIG. 8 is a heat map showing experimental data for the gate contact 78layout of FIGS. 7A and 7B. In FIG. 8 , the X-axis plots spacing betweenadjacent fins 52 (e.g., the distance D₁), the Y-axis plots spacingbetween a gate contact 78 and an adjacent fin 52 (e.g., the distanceD₂), and values on the heat map plot the relative contact resistance.For example, the X-axis can be in a range of about 15 to about 75, andthe Y-axis can be in a range of about 5 to about 20. As shown, when thedistance D₁ was less than the first predetermined threshold T₁, allvalues for the distance D₂ resulted in a low contact resistance.However, when the distance D₁ was greater than the first predeterminedthreshold T₁, values for the distance D₂ that were greater than thesecond predetermined threshold T₂ resulted in a rapidly-increasingrelative contact resistance along gradient G₁. For example, inembodiments where the width W₂ is about 6 nm, the distance D₂ isconstrained to being less than about 70 nm when the distance D₁ isgreater than or equal to about 216 nm, and the distance D₂ isunconstrained when the distance D₁ is less than about 216 nm.Constraining the distances according to the experimental results shownin FIG. 8 allows the gate contacts 78 to be placed without substantiallyincreasing the contact resistance.

The embodiments described in FIGS. 7A and 7B may be combined on a samesubstrate. For example, in a first region of the substrate, the distanceD₁ between fins 52 may be constrained to less than the firstpredetermined threshold T₁. Such a constraint may prevent or reduce theformation of voids 82 in the first region. Likewise, in a second regionof the substrate, the distance D₁ between fins 52 may be greater thanthe first predetermined threshold T₁, and the distance D₂ between thefins 52 and gate contacts 78 is constrained to less than the secondpredetermined threshold T₂. Such a constraint may help avoid forming thegate contacts 78 on voids 82 in the second region.

As used herein, “constraining” the widths W₁ and W₂ refers to imposingconstraints during a design process for the fins 52 and gate contacts78. After the design process is completed, the design may be stored in,e.g., a cell library. The cell library may then be used to manufacture acorresponding FinFET.

FIG. 9A illustrates a gate contact 78 layout, in accordance with someother embodiments. FIG. 9A is a top-down view, showing some features ofthe structure of FIGS. 6A through 6C. In particular, two of the fins 52are shown, with each respective fin 52 being adjacent the end of themetal lines that form the gate stacks 74. The gate contacts 78physically couple the gate stacks 74, and are disposed a distance D₃from the ends of the metal lines.

When forming the gate stacks 74, voids 82 may also be formed at the endsof the metal lines. As noted above, the dummy gate dielectrics 58 anddummy gate electrodes 60 are replaced by forming recesses 68 exposingchannel regions of the fins 52, and forming the gate stacks 74 in therecesses 68. The etching step(s) for forming the recesses 68 results inthe recesses 68 having rounded ends. As noted above, the gate stacks 74are formed by depositing a conductive material in the recesses 68, suchas with an ALD process. The rounded ends of the recesses 68 are narrowerthan the main portions of the recesses 68, and the ALD process may haveimperfect gap-filling properties. As such, voids 82 may be formed atends of the gate stacks 74, proximate the rounded ends. The voids 82 aredisposed a distance D₄ from the ends of the metal lines. In someembodiments, the distance D₄ is in the range of about 50 nm to about 90nm.

In accordance with some embodiments, the gate contacts 78 are formedphysically coupling portions of the gate stacks 74 that aresubstantially free from voids 82. The contact resistance of the gatecontacts 78 may thus be decreased. During a design process, the distanceD₃ is determined according to the width W₂ of the gate stacks 74 and thewidth W₃ of the gate contacts 78. In particular, the distance D₃ isgreater than the distance D₄, and at least the sum of half of the widthW₂ and half of the width W₃, e.g., D₃ is constrained according to D₃>D₄and D₃>0.5*W₂+0.5*W₃. In some embodiments, the distance D₃ is in therange of about 91 nm to about 500 nm. As such, when the gate contacts 78are formed, the voids 82 are laterally disposed between the gatecontacts 78 and the ends of the metal lines. The distance D₃ is largeenough to help avoid formation of the gate contacts 78 on the voids 82.

The distance D₁ between fins 52 at the ends of the metal lines may belarger, to accommodate the larger distance D₃. In particular, thedistance D₁ in the embodiment of FIG. 9A is larger than the distance D₁in the embodiments of FIGS. 7A and 7B. In some embodiments, the distanceD₁ between fins 52 at the ends of the metal lines is in the range ofabout 442 nm to about 1000 nm.

FIG. 9B illustrates a gate contact 78 layout, in accordance with someother embodiments. FIG. 9B is a top-down view, showing some features ofthe structure of FIGS. 6A through 6C. The embodiment of FIG. 9B issimilar to the embodiment of FIG. 9A, but includes gate stacks 74 ofmultiple widths. For example, a first set of gate stacks 74A may have awidth W_(2,1), and a second set of gate stacks 74B may have a widthW_(2,2), with the width W_(2,1) being greater than the width W_(2,2). Insome embodiments, the width W_(2,1) is in the range of about 67 nm toabout 151 nm, and the width W_(2,2) is in the range of about 67 nm toabout 151 nm.

FIGS. 10 through 12 are top-down views of intermediate stages in aprocess for forming the gate contacts 78, in accordance with someembodiments. FIG. 13 is a three-dimensional view of the resultingstructure. Multiple gate stacks 74 are shown, with each respective gatestack 74 initially being formed as a continuous metal line extendingover two fins 52. The gate stacks 74 may be formed to originally spanthe fins 52 of multiple transistors (where each transistor may includeone or a plurality of fins 52). The distance D₁ between fins 52 islarge, to accommodate a line cut that will be subsequently performed. Inparticular, the distance D₁ in the embodiment of FIGS. 10 through 13 islarger than the distance D₁ in the embodiments of FIGS. 7A and 7B. Insome embodiments, the distance D₁ between fins 52 is in the range ofabout 350 nm to about 1000 nm.

In FIG. 10 , each respective gate stack 74 is cut in a region 84 to forman opening 86. The opening 86 can also be formed in dielectric layersaround the gate stacks 74, such as the first ILD 66. After the cut, thecontinuous metal lines are broken into smaller metal lines. The cut maybe performed by acceptable photolithography and etching processes. Forexample, a photoresist may be formed, and patterned to expose the region84. One or more etching processes may then be performed on the gatestacks 74, using the patterned photoresist as an etching mask. Thephotoresist may then be removed, such as by an ashing process. Afterbeing cut, each gate stack 74 may span the fins 52 of a singletransistor (where the transistor may include one or a plurality of fins52). By forming a continuous metal line and cutting it, the formation ofvoids at the ends of the metal lines may be avoided. The ends of eachgate stack 74 are thus free from voids.

In FIG. 11 , the opening 86 is filled with a dielectric material 88. Thedielectric material 88 may be silicon nitride, silicon oxynitride,silicon oxide, silicon carbide, or the like, and may be formed byblanket depositing a dielectric layer and planarizing the dielectriclayer to remove portions of the dielectric material 88 outside of theopening 86. Remaining portions of the dielectric material 88 isolate thecut metal lines from one another.

In FIG. 12 , the gate contacts 78 are formed, contacting the cut gatestacks 74. The gate contacts 78 physically couple the cut gate stacks74, and are disposed a same distance D₃ from the ends of the metal lines(e.g., from the dielectric material 88). Because the formation of voidshas been avoided, the distance D₃ in the embodiment of FIGS. 10 through13 may be smaller than the distance D₃ in the embodiments of FIGS. 9Aand 9B. In some embodiments, the distance D₃ is in the range of about 91nm to about 500 nm. The gate contacts 78 may be formed at the ends ofthe cut gate stacks 74 without the need to avoid contacting voids.

Embodiments may achieve advantages. By constraining the distance D₂between the fins 52 and gate contacts 78 (see FIG. 7B) for fins 52spaced by a large distance D₁, formation of the gate contacts 78 onvoids 82 may be avoided. By increasing the distance D₃ between the gatecontacts 78 and the ends of the gate stack metal lines, formation of thegate contacts 78 on voids 82 may be further avoided. The contact area ofthe gate contacts 78 may thus be increased, thereby decreasing thecontact resistance of the gate contacts 78. Finally, by initiallyforming longer gate stack metal lines and cutting the lines, theformation of voids may be avoided, and the gate contacts 78 may beformed at the ends of the cut gate stacks 74 without the need to avoidcontacting voids.

In an embodiment, a method includes: forming a first fin extending froma substrate; forming a second fin extending from the substrate, thesecond fin being spaced apart from the first fin by a first distance;forming a metal gate stack over the first fin and the second fin;depositing a first inter-layer dielectric over the metal gate stack; andforming a gate contact extending through the first inter-layerdielectric to physically contact the metal gate stack, the gate contactbeing laterally disposed between the first fin and the second fin, thegate contact being spaced apart from the first fin by a second distance,where the second distance is less than a second predetermined thresholdwhen the first distance is greater than or equal to a firstpredetermined threshold.

In some embodiments of the method, the metal gate stack has multiplewidths, and a portion of the metal gate stack with a narrowest width ofthe multiple widths is disposed over the first fin. In some embodimentsof the method, the first predetermined threshold is in a range of 35 to40 times the narrowest width of the metal gate stack. In someembodiments of the method, the second predetermined threshold is in arange of 10 to 13 times the narrowest width of the metal gate stack. Insome embodiments of the method, the narrowest width of the metal gatestack is in a range of 6 nm to 300 nm. In some embodiments, the methodfurther includes: depositing a second inter-layer dielectric around themetal gate stack, where after the second inter-layer dielectric isformed, a first portion of the metal gate stack includes a void. In someembodiments of the method, the gate contact physically contacts a secondportion of the metal gate stack, the first portion of the metal gatestack being distal the first fin, the second portion of the metal gatestack being proximate the first fin. In some embodiments of the method,the first portion of the metal gate stack and the second portion of themetal gate stack are laterally disposed between the first fin and thesecond fin.

In an embodiment, a method includes: forming a first fin extending froma substrate; forming a dummy gate stack over the first fin; depositing afirst inter-layer dielectric along the dummy gate stack; replacing thedummy gate stack with a metal gate stack, an end of the metal gate stackbeing rounded, the metal gate stack including a void, the void beingdisposed a first distance from the rounded end of the metal gate stack;forming a second inter-layer dielectric over the metal gate stack andthe first inter-layer dielectric; and forming a gate contact extendingthrough the second inter-layer dielectric to physically contact a firstportion of the metal gate stack, the first portion of the metal gatestack being disposed a second distance from the rounded end of the metalgate stack, the second distance being greater than the first distance.

In some embodiments of the method, the first distance is in a range of50 nm to 90 nm, and the second distance is in a range of 91 nm to 500nm. In some embodiments of the method, the first fin has a first width,the gate contact has a second width, and the second distance is greaterthan a sum of half of the first width and half of the second width. Insome embodiments of the method, the first fin is adjacent the roundedend of the metal gate stack. In some embodiments of the method,replacing the dummy gate stack with the metal gate stack includes:etching the dummy gate stack to form a recess having a rounded end; andfilling the recess with a metal, the void being formed during thefilling.

In an embodiment, a method includes: forming a first fin extending froma substrate; forming a second fin extending from the substrate; forminga metal line over the first fin and the second fin; cutting the metalline along a first region to separate the metal line into a first metalgate stack and a second metal gate stack, the first metal gate stackbeing over the first fin, the second metal gate stack being over thesecond fin; depositing a first inter-layer dielectric over the firstmetal gate stack and the second metal gate stack; forming a first gatecontact extending through the first inter-layer dielectric to physicallycontact the first metal gate stack, the first gate contact beingdisposed a first distance from the first region; and forming a secondgate contact extending through the first inter-layer dielectric tophysically contact the second metal gate stack, the second gate contactbeing disposed the first distance from the first region.

In some embodiments of the method, cutting the metal line includes:etching the metal line in the first region to form a first openingthrough the metal line; and forming a dielectric material in the firstopening. In some embodiments of the method, the first inter-layerdielectric is further deposited over the dielectric material. In someembodiments, the method further includes: forming gate spacers adjacentthe metal line, the dielectric material extending between the gatespacers. In some embodiments, the method further includes: forming asecond inter-layer dielectric around the gate spacers. In someembodiments of the method, the first fin and the first metal gate stackare part of a first transistor, and where the second fin and the secondmetal gate stack are part of a second transistor. In some embodiments ofthe method, ends of the first metal gate stack and the second metal gatestack are free from voids.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A device comprising: a first metal gate stackover a substrate; a second metal gate stack over the substrate; adielectric material between a first end of the first metal gate stackand a second end of the second metal gate stack; an inter-layerdielectric over the dielectric material, the first metal gate stack, andthe second metal gate stack, a first gate contact extending through theinter-layer dielectric to physically contacting the first metal gatestack; and a second gate contact extending through the inter-layerdielectric to physically contacting the second metal gate stack, whereinhalf of a distance between the first gate contact and the second gatecontact is larger than a distance between the first gate contact and thedielectric material and is larger than a distance between the secondgate contact and the dielectric material.
 2. The device of claim 1,wherein a top surface of the dielectric material is planar with a topsurface of the first metal gate stack and a top surface of the secondmetal gate stack.
 3. The device of claim 1, wherein the distance betweenthe first gate contact and the dielectric material is in a range ofabout 91 nm to about 500 nm, and the distance between the second gatecontact and the dielectric material is in a range of about 91 nm toabout 500 nm.
 4. The device of claim 1, wherein the first metal gatestack has a first width, the second metal gate stack has a second width,the first width is less than the distance between the first gate contactand the dielectric material, and the second width is less than thedistance between the second gate contact and the dielectric material. 5.The device of claim 1, further comprising: a gate spacer adjacent thefirst metal gate stack, the second metal gate stack, and the dielectricmaterial.
 6. The device of claim 1, wherein the first end of the firstmetal gate stack and the second end of the second metal gate stack arefree from voids.
 7. A device comprising: a first metal gate stack over asubstrate; a second metal gate stack over the substrate; a dielectricmaterial between the first metal gate stack and the second metal gatestack, a top surface of the dielectric material being planar with a topsurface of the first metal gate stack and a top surface of the secondmetal gate stack; an inter-layer dielectric over the top surface of thedielectric material, the top surface of the first metal gate stack, andthe top surface of the second metal gate stack, a first gate contactextending through the inter-layer dielectric to physically contact thefirst metal gate stack, the first gate contact being disposed a firstdistance from the dielectric material; and a second gate contactextending through the inter-layer dielectric to physically contact thesecond metal gate stack, the second gate contact being disposed a seconddistance from the dielectric material, wherein the first distance andthe second distance are substantially equal.
 8. The device of claim 7,further comprising: a first fin extending from the substrate, the firstmetal gate stack disposed over the first fin; and a second fin extendingfrom the substrate, the second metal gate stack disposed over the secondfin, the first gate contact and the second gate contact each beingdisposed between the first fin and the second fin.
 9. The device ofclaim 7, wherein the first metal gate stack and the second metal gatestack are parts of different transistors.
 10. The device of claim 7,wherein ends of the first metal gate stack and the second metal gatestack are free from voids.
 11. The device of claim 7, wherein the firstmetal gate stack has a first width, the second metal gate stack has asecond width, the first gate contact has a third width, the second gatecontact has a fourth width, the first distance is greater than a sum ofhalf of the first width and half of the third width, and the seconddistance is greater than a sum of half of the second width and half ofthe fourth width.
 12. The device of claim 11, wherein the third widthand the fourth width are substantially equal.
 13. The device of claim 7,wherein the first distance and the second distance are each in a rangeof about 91 nm to about 500 nm.
 14. A device comprising: a first finextending from a substrate; a second fin extending from the substrate; afirst metal gate stack over the first fin, the first metal gate stackhaving a first width; a second metal gate stack over the second fin, thesecond metal gate stack having a second width; an inter-layer dielectricover the first metal gate stack and the second metal gate stack; a firstgate contact extending through the inter-layer dielectric to physicallycontact the first metal gate stack, the first gate contact having athird width, the first gate contact being disposed a first distance froman first end of the first metal gate stack, the first distance beinggreater than a sum of half of the first width and half of the thirdwidth; and a second gate contact extending through the inter-layerdielectric to physically contact the second metal gate stack, the secondgate contact having a fourth width, the second gate contact beingdisposed a second distance from an second end of the second metal gatestack, the second distance being greater than a sum of half of thesecond width and half of the fourth width.
 15. The device of claim 14,wherein the first distance and the second distance are each in a rangeof about 91 nm to about 500 nm.
 16. The device of claim 14, wherein thefirst gate contact and the second gate contact are each disposed betweenthe first fin and the second fin.
 17. The device of claim 14, whereinthe first fin and the first metal gate stack are part of a firsttransistor, and the second fin and the second metal gate stack are partof a second transistor.
 18. The device of claim 14, wherein the firstdistance is substantially equal to the second distance.
 19. The deviceof claim 14, wherein the first metal gate stack comprises a first voidbetween the first gate contact and the first end of the first metal gatestack, and the second metal gate stack comprises a second void betweenthe second gate contact and the second end of the second metal gatestack.
 20. The device of claim 14, wherein the first end of the firstmetal gate stack is a first rounded end, and the second end of thesecond metal gate stack is a second rounded end.